The present invention relates to methods for preparation of certain m-aminophenols which are useful to prepare dyes. In particular, the aminophenols are useful for preparing dyes having use in laser applications, printing inks, fluorescent signs and recreational equipment, fluorescent tags in diagnostic methods, as well as in other products and methods where fluorescent materials are used.
Dyes having use in laser applications are disclosed in U.S. Pat. Nos. 3,932,415, and 4,005,092, both of which in particular disclose the preparation of 8-hydroxy- 2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizine and a method for converting it to 9-(2-carboxyphenyl)2,3,6,7,12,13,16,17-octahydro-1H,5H,11H,15H-diquinolizi no-[1,9-bc;1',9'-h,i]xanthylium chloride (also known as Rhodamine 101). U.S. Pat. Nos. 4,005,092, 3,932,415 and 3,822,270 further disclose preparation of 1,2,3,4,8,9,10,11-octahydro-6-(2-carboxyphenyl)-dipyrido[3,2-b;2',3'-i]xan thylium perchlorate using 7-hydroxy-1,2,3,4-tetrahydroquinoline as a starting material. J. V. Braun, Chem. Ber., 47, 492 (1914) discloses preparation of 7-hydroxy1,2,3,4-tetrahydroquinoline by a series of steps consisting of nitration of 1,2,3,4-tetrahydroquinoline to form the 7-nitro derivative, benzoylation of the amine, reduction of the nitro group to the 7-amino derivative, diazotization to the 7-phenol, and hydrolysis of the benzoyl group. Hammond and Atkins, J. Heterocyclic Chem., 12, 1061 (1975), disclose the preparation of 1,2,3,4-tetrahydro-7-hydroxyquinoline by hydrogenation of 7-hydroxy-quinoline.
Sulfonation by fuming sulfuric acid to form the sulfonate followed by alkaline fusion has been described for making m-aminophenol, m-dimethylaminophenol and m-diethylaminophenol (German Pat. No. 44,792 (1888)), m-methylaminophenol and m-ethylaminophenol (German Pat. No. 48,151 (1889)), 3-methylamino-4-cresol(OH-1), 3-ethylamino-4-cresol(OH-1) (German Pat. No. 69,074 (1892)). However, such procedures have heretofore not been applied to 1-alkyl-1,2,3,4-tetrahydroquinoline.
The above known methods for preparing 1-alkyl-1,2,3,4-tetrahydroquinolines and 7-hydroxy-1,2,3,4-tetrahydroquinolines have drawbacks for preparing aminophenols in large quantities because they are lengthy and inefficient due to a low overall yield and process complexity.
It is thus desirable to have a method for producing N-substituted-7-hydroxyquinolines which is not only simple and efficient but which also results in overall high yield of the desired product utilizing readily available and inexpensive starting materials.